The present invention relates to a spark ignition internal combustion engine for automobiles, having a system for controlling the emission of noxious gases from the exhaust comprising the combination of a plurality of devices including an after burner for the exhaust gases, the function of which is to reduce the amount of carbon monoxide and unburnt hydrocarbons in the exhaust gases, means for improving the carburation when the engine is cold (this means also functioning to improve the fuel consumption when the engine is hot), means for recycling at least part of the exhaust gases to the induction side of the engine, and means for reducing the emission of pollutants during deceleration of the engine.
In an attempt to reduce atmospheric pollution many countries now have laws which require internal combustion engines to be fitted with various devices for the purpose of reducing, as far as possible, the emission of pollutants, and for improving the fuel consumption. In order to comply with these laws many automobile manufacturers fit their vehicles with after burner means for effecting further combustion of the exhaust gases by admitting into the exhaust system further combustion air so that the combustion of carbon monoxide and hydrocarbons is as complete as possible. Further measures include the addition into the fresh fuel/air mixture which is about to be burnt a small part of the hot exhaust gases, which thus reduces the formation of oxides of nitrogen, and the introduction of supplementary air into the induction manifold during deceleration of the engine whereby to reduce the fuel content in the fuel/air mixture thereby reducing the emission of unburnt hydrocarbons which are an important part of the pollutants in the exhaust gases emitted in these conditions.
However, in certain transitional operating conditions of an internal combustion engine some of the above mentioned measures can cause engine operating difficulties, particularly during starting of the engine, and in running conditions when the engine is cold.